Gravitational and Electric Fields Flashcards
What is a force field?
A region which a body experiences a non-contact force
Give an example of a force field
Gravitational field
What causes a force field?
Interactions between objects or particles e.g. between static or moving charges
What can be said about the affect of gravitational fields around objects of large mass?
Only objects with a large mass, such as planets or stars, have gravitational fields that produce a significant effect
What can be said about the affect of gravitational fields around objects of small mass?
Small objects still have a gravitational field that attracts other objects. but the effect is too weak to be noticeable
How do you represent force fields?
With vector lines, showing the direction of the force they would exert on an object placed in that field
Describe the Earth’s gravitational field
It is radial, so all the lines of force meet in the centre of the Earth
The further apart the vector lines on a force field diagram, the…?
Smaller the force an object placed in the field would experience
Is the force experienced by an object in a gravitational field attractive or repulsive?
Always attractive
What is a point mass?
An object that behaves as if all their mass is concentrated at the centre
What is the equation for Newton’s Law of Gravitation?
F = Gm1m2 / r^2
F: Magnitude of force G: Gravitational constant m1: Mass of 1st object m2: Mass of 2nd object r: Distance between the centres of 2 masses
Describe the proportionality for the Law of Gravitation
It is an inverse square law, so F ∝ 1/r^2
For Newton’s 3rd Law, why don’t we notice the equal and opposite force of the Earth accelerating towards us when we’re falling to the ground?
Because the mass of the Earth is so much larger, F=ma, that the acceleration becomes so incredibly small it’s negligible
Describe the magnitude of the force when the distance between the 2 masses is doubled
Because F ∝ 1/r^2, the force will be 1/4 the strength of the original force
Why is the law of gravitation an inverse square law?
Because it’s radial, so the force at any point with a set distance r will be the same
What is the gravitational field strength?
The force per unit mass
What is the equation for gravitational field strength?
g = F/m
g: Gravitational field strength
F: Force experienced by mass
m: Mass
What are the units of gravitational field strength?
Nkg^-1
What is the approximate value of g at the Earths surface?
9.81 Nkg^-1
What is the equation for the magnitude of a radial gravitational field strength?
g = GM/r^2
g: Magnitude of gravitational field strength
G: Gravitational constant
M: Mass of object creating gravitational field
r: Distance from the centre or distance from point mass
Describe the gravitational field of a point mass
It is a radial gravitational field
Describe what happens to g as you get further away from the Earths surface
g is greatest at the Earths surface, then decreases rapidly as r increases and you move further away from the centre
How do you combine gravitational fields?
Because they’re vectors, you can add them up to find the combined effect of more than one object
What is the direction of an objects gravitational field?
Towards the object, because it’s an attractive force